The present invention relates to a semiconductor device that is implemented in an IGBT (Insulated Gate Bipolar Transistor) module, or to its assembled structure.
The assembled structure of a conventional semiconductor device is shown in FIG. 2 in conjunction with the IGBT module described above. In the figure, 1 is an IGBT chip element; 2 is a ceramic substrate on which the chip element is mounted; 3 is a radiating metal base on which the ceramic substrate 2 is installed; 4 is an enclosure or resin case as a terminal case; 4a is a top cover for the resin case 4; 5 is an emitter terminal frame for an externally drawn terminal; 6 is a collector terminal frame; 7 is a gate terminal frame; 8 is a bonding wire that connects the IGBT terminal 1 and a conductor pattern 2a on the ceramic substrate 2; and 9 is a silicone gel (gel type sealing resin) that fills the resin case 4. In the figure, reference symbol E designates an emitter terminal, C denotes a collector terminal, and G indicates a gate terminal.
The terminal frames 5, 6 and 7 are drawn upwardly from the ceramic substrate 2 and installed inside the resin case 4, and their leg pieces 5a, 6a and 7a are soldered to a conductor pattern 2a corresponding to the emitter, collector and gate formed on the ceramic substrate 2. The emitter and collector main terminal pieces 5b and 6b are welded to the emitter and collector terminal frames 5 and 6 respectively, protrude vertically as main circuit terminals through the case cover 4a, and are drawn from the top surface of the resin case 4. After the resin case 4 has been bonded to the metal base 3, the resin case is filled with liquid silicone and the top cover 4a is then installed. Subsequently, a heating process is executed to gel the silicone to resin-seal the chip element 1 and the terminal frames 5, 6 and 7 in order to provide the required insulation.
Only one chip element 1 is shown in the figure, but in the actual IGBT module, multiple ceramic substrates 2 on which multiple IGBT chip elements 1 are mounted are juxtaposed on the metal base 3 with the chip elements 1 being connected in parallel via the terminal frames 5, 6 and 7 extending across the ceramic substrates 2, thereby constituting the IGBT module with a large capacity.
In the semiconductor device with the above structure, the emitter and collector terminal frames 5 and 6, which are the externally drawn terminals of the main circuit, are installed in proximity in a limited space inside the resin case 4, and the main terminal pieces 5b and 6b protruding vertically from the terminal frames are drawn from the top surface of the case in such a way as to extend parallel to each other. Therefore, to fill the resin case 4 with the silicone gel to provide the required dielectric voltage resistance between the terminals of different polarities, the amount of silicone gel 9 with which the case 4 is filled must be set so that the terminal frames 5 and 6 are both immersed in the silicone gel 9.
In this case, in a module with the height of the resin case 4 almost the same as the wiring height of the terminal frames installed inside the resin case 4 in order to minimize the thickness of a package for the module, the filling level H2 of the silicone gel 9 in the resin case 4 is almost the same as the height of the top surface of the resin case 4.
Therefore, when the resin case is filled with liquid silicone during an assembly process for the semiconductor device or a resin-filled module assembly is transferred to the subsequent gelling process via a conveyor, slight vibration or impact often causes the liquid silicone to overflow from the enclosure resin case 4, and the silicone sticks to the outer surface of the package and degrades the appearance of the product. This is one of the causes of a decrease in product yield.
This invention is provided in view of the above point. The object is to provide a semiconductor device with improved structure so as to reduce the amount of a gel sealing resin in a resin case to prevent the sealing resin from overflowing during the assembly process while mutually insulating terminal frames of different polarities.